1. Field of the Invention
The present invention relates to packet networks, and, more particularly, to adaptive routing of packets in a communications network based on quality of service provisioning.
2. Description of the Related Art
Packet network service providers, such as those providing Internet Protocol (IP) networks, are presently developing and providing differentiated services. In particular, service providers are interested in differentiated services as part of provisioning and maintaining networks for customers with a variety of voice and data needs. For example, virtual private networks (VPNs) allow service providers to establish and tear-down connections for a large number of users, while billing only one customer or client (e.g., a large corporation or government agency) for the service. However, the customer or client may require a certain amount of guaranteed bandwidth, minimum transport delay, or other metric for some or all of the data transported through the VPN. Service providers generally desire a higher revenue for data transported through the VPN when a customer demands such differentiated services.
In the art, the term xe2x80x9cphysical pathxe2x80x9d denotes the path between source and destination pairs for a given communication stream of data, or packet flow, together with intermediate nodes, if any, and the physical links that connect the nodes. In networks of practical size and complexity, many sets of multiple physical paths may exist, each provisioned to carry one or more corresponding packet flows. The network operator may specify a predetermined bandwidth for the corresponding stream or packet flow along each link of the possible physical paths. The specified bandwidth may equal the full bandwidth, or some quantity less than the full bandwidth, or no bandwidth at all. Although a physical path may exist between a source and destination pair, the full bandwidth of the physical path links may be unavailable for the corresponding packet flow.
In addition, the term xe2x80x9clogical pathxe2x80x9d (also called a xe2x80x9cvirtual pathxe2x80x9d) denotes a path between a given source and destination pair as defined by connection metrics, such as delay or bandwidth. Logical (virtual) paths are not determined purely by physical considerations, but instead are partly defined by parameters that may be specified and/or changed. Individual virtual paths may require less than the fully assigned bandwidth physically available on the physical links that the paths occupy. Thus, several virtual paths may co-exist along part or all of a physical path, allowing each physical link of the network to simultaneously support several virtual paths.
Packet networks that provide differentiated services generally include a routing method that allows the network to determine a logical path through the network from a given source to a given destination. The routing method may be part of a process performed in each router of the network. Each router may learn the network topology by exchanging link and router information between directly connected routers. Once the router determines the network topology, the router may employ a path-selection process that determines the logical path through a network between the source and destination pair over the physical links according to-predefined connection metrics. Each router determines the same logical path through the packet network given the same information. Packets received by each router are then routed along the determined path.
A standard protocol employed by IP networks to determine network topology and link routing is the Open Shortest Path First (OSPF) protocol, as outlined in J. Moy, xe2x80x9cOSPF Version 2,xe2x80x9d Internet Draft, Request for Comment (RFC) 2178, July 1997. The OSPF protocol employs the destination (i.e., shortest path to destination) as the metric for the path-selection process. However, with destination as the only metric, only a xe2x80x9cbest effortxe2x80x9d is employed to route packet flows. Best effort implies that, while the packets are re-routed, no other QoS provisioning commitment, such as minimum bandwidth, delay or loss, applies to the packet flow. Routers of the prior art may route packets based on other factors, such as available bandwidth. However, when the OSPF protocol is employed as the routing method, distribution of packet flows over the links is based on shortest path and not provisioned QoS commitments.
Routing methods may determine logical paths and allocate corresponding bandwidth to the links in the network, with such allocation according to the source and destination pair, subnetwork, and class of service. This path-selection method or determination may be referred to as logical network design. One important element of logical network design is selection of a set of physical paths through the network having sufficient capacity for carrying the estimated traffic of a communication stream or packet flow. The routing method may base the determination on such factors as the network topology, the currently available buffer space at the nodes, and the currently available link capacities.
Significantly, the network operator may have QoS commitments with its customers, such as guaranteed bandwidth or maximum cell-loss probability. The path-selection process may account for such commitments, but the routing method may require simplifications to characterize variable traffic characteristics in a form that the routing method can use for logical path determination. For example, certain networks, particularly high-speed networks, may support the networking protocol known as asynchronous transfer mode (ATM). Such high-speed networks typically carry multiple services having different traffic characteristics, including both constant bit rate traffic and variable bit rate traffic. An important simplification for routing methods considering variable bit rate traffic in networks, such as ATM networks, is provided by the concept of xe2x80x9ceffective bandwidth.xe2x80x9d
Effective bandwidth of a packet flow defines the bandwidth of the packet flow in terms of the node buffer size and the average and peak rates of the packet flow, assuming the node operates with a leaky bucket regulator. An effective bandwidth may be determined for each packet flow, of a network where the packet flows are multiplexable, the total effective bandwidth of all packet flows is less than or equal to the total network capacity, and the packet flows exhibit loss-less performance. (i.e., the packet flows may be rearranged over multiple physical paths while maintaining desired delay or bandwidth for each packet flow). For networks having both multiplexable and non-muliplexable packet flows, the two types of traffic may be separately analyzed, with portions of the total network capacity allocated to each traffic type.
Effective bandwidth, and allocation of bandwidth and buffer capacity based on effective bandwidth, is described in detail in A. Elwalid et al., xe2x80x9cA New Approach For Allocating Buffers and Bandwidth to Heterogeneous, Regulated Traffic in an ATM Node,xe2x80x9d IEEE Journal on Selected Areas in Communications, Vol. 13, No. 6, (August 1995) 1115-1127 (incorporated herein by reference and referred to as xe2x80x9cElwalid et al.xe2x80x9d). A routing algorithm that accounts for variable bit rate traffic in ATM networks with effective bandwidth, is described in detail in U.S. Pat. No. 5,838,663, issued on Nov. 11, 1998 entitled xe2x80x9cA Method for Admission Control and Routing by Allocating Network Resources in Network Nodesxe2x80x9d, which is incorporated herein by reference.
Once logical paths are specified, the routers of the network generally must support at least two types of messages for the packet flows and network administration: data messages and control messages. Data messages are packets containing user information transported between the source and destination pair. Control messages are messages interpreted by network elements, such as the routers, to administer connections and exchange network information. These control messages may be employed to ensure that the packets are interpreted and routed in a manner that provides the desired commitment of the path-selection process. Control messages may be included in packet headers, or may be separate and distinct packets.
One approach of the prior art for providing differentiated services employs type-of-service (TOS) bits defined in the packet header, or TOS addressed metrics in the packet payload. The TOS bits are interpreted by routers within the network in an agreed upon manner so that each network node provides the desired QoS commitments of the service when routing the packet flow. This approach may allow for distribution of each and all resource requests to all nodes of the network. Alternate approaches may be reservation-based and may employ signaling to reserve network resources for the duration of a packet flow, or packet flow aggregates. A protocol to signal reservation of network resources in a network is the Reservation Setup Protocol (RSVP). RSVP, as an example, may be used in conjunction with service models, such as guaranteed rate and controlled load service models, to request the desired QoS commitments for certain flows.
Once the connection is established, the router includes a routing fabric to physically route packets received at input ports to specific output ports for transport to the next node or destination. Packet filters may be employed with the routing fabric to determine actions to be taken for packets having certain source and destination addresses arriving at the router. Actions may be that routing of packets sent from one or more of specified sources is denied (e.g., actions for xe2x80x9cfirewallxe2x80x9d or security purposes), or that a specific action is to be taken for that packet having a specified source address (e.g., actions for routing to a specific, alternate destination). The router may be provided with a table or list of filter rules specifying the desired actions for corresponding field addresses. The packet filter allows the router to associate fields of received packets with the table or list entries.
Packets comprise, for example, a header and a payload that may include user data. A header of the packet includes fields or parameters, such as a source address where the data originates and at least one destination address where the data is to be routed. Another parameter in the header may be a protocol type identifying a particular protocol employed in the communication network. Source and destination addresses may be logical addresses of end hosts. The header may also include, for example, certain types of flags in accordance with protocol type, such as TCP, depending upon the receiver or transmitter application.
The IP packet header fields typically contain up to 128 bits of parameter information, including source and destination addresses, physical source and destination port numbers, interface number, protocol type, etc. Filter rules may also specify, for example, that for received packets with fields in the header specifying a particular destination address, the packet should or should not be forwarded through specific output links or output ports. Thus, a variety of filter rules may be implemented based on packet field information. For example, such filter rules might be based on 1) source addresses; 2) destination addresses; 3) source ports; 4) destination ports; and/or 5) any combination of these fields. Consequently, such packet filtering may be employed by layer four switching applications.
Each of the fields or parameters in the header may be represented as points along an axis of a dimension. The general packet classification problem of a packet filter may then be modeled as a point-location in a multi-dimensional space. One or more field values of the packet define a point in the multi-dimensional space. A packet filter rule associated with a range of values in each dimension defines an object in the multi-dimensional space.
A point-location algorithm in a multi-dimensional space with multi-dimensional objects finds the object that a particular point belongs to. Given a received point EP={E1, E2, . . . ED} in a space having D dimensions, the point-location algorithm finds one or more of a set of n D-dimensional objects including the point EP (n being an integer greater then 0). The general case of D greater than 3 dimensions may be considered for the problem of packet classification. For the special case of two dimensions, the filter rules defined for field ranges are modeled as objects in two dimensions, forming rectangles in the 2-dimensional space. The specific case of filter rules defined for field ranges that are modeled as objects in two dimensions may correspond to switching of packets through a routing fabric based on source address/port and destination address/port.
Once the physical and logical paths through the network are determined, network resources are reserved through the nodes of the network when a link is established and packet flows between source and destination pairs begin. However, when a link is broken, such as by a disconnected T 1, T3, or fiber-optic connection to an interface card of the network node, or when a node fails, such as when a router fails, the routing mechanism must determine alternate paths through the network to re-establish the packet flows.
Since packet network links are generally in a state of flux, service providers may not be able to effectively provide QoS provisioning, and hence receive revenue, when re-routing does not effectively preserve the QoS commitments to the VPN. Routing mechanisms of the prior art currently route packets through the network based on destination address. Reservation-based protocols alone may only request bandwidth for a link to be established, with no guarantee of success of the request.
The present invention relates to adaptive routing, and more particularly to generating new routing paths through a router of a packet network. Generating new routing paths may occur when new paths for packet flows are desired because a trigger event, such as a node/link failure or a network topology/provisioning change, occurred in the packet network. In accordance with the present invention, 1) network topology information and 2) quality of service (QoS) provisioning information are collected for each packet flow through one or more routers of the packet network. A path for each packet flow is determined using a general routing optimization method, such as a multicommodity flow routing method, based on the QoS provisioning and network topology information. A set of one or more filter rules is generated for the router based on the one or more paths for the one or more packet flows passing through the router, each filter rule defining a physical path for one or more packet flows through the router. A selected filter rule is applied to each packet of a packet flow to cause each packet to traverse the corresponding path through the router.
The present invention may allow for adaptive routing using packet classification with filter rules. New path routing may be generated as provisioning entries generated by a multicommodity flow-based routing method using network topology information and quality of service (QoS) provisioning information. The provisioning entries may then be translated into filter rules of a packet classifier that implements the new routing paths, thereby implementing adaptive routing in accordance with the present invention.